Thermal overload switch



Nov. 20, 1956 D. E. MORAN 2,771,528

THERMAL OVERLOAD SWITCH Filed Feb. '25, 1954 [n l/en tor.- Don E/Vorarz,

his Attorney.

United States Patent THERMAL OVERLOAD SWITCH Don E. Moran, Morrison,11]., assignor to General Electric Company, a corporation of New YorkApplication February 25, 1954, Serial No. 412,468

Claims. (Cl. 200-122) This invention relates to thermal overloadswitches and more particularly to thermal overload switches of theautomatically resetting type.

Thermal overload switches are frequently used to provide thermalprotection for electrical apparatus, such as electric motors. One formof such a device incorporates a bimetallic element carrying a movablecontact which cooperates with a stationary contact, the bimetallicelement and the stationary contact being serially connected in thecircuit to be protected. A heater may also be arranged in heat transferrelationship to the bimetallic element and may be arranged either forconnection in series with the bimetallic element and the stationarycontact, or in another circuit. Thus, such a device may be maderesponsive to both the supporting ambient temperature and overloadcurrent. It is desirable in some applications for such devices that theswitch after opening in response to an overload, automatically resetitself when the surrounding ambient temperature has fallen to apredetermined level. It is further desirable that both the tripping andresetting temperatures be readily and independently adjustable and thatthe device be simple, easy to assemble and inexpensive.

It is therefore an object of this invention to provide a thermaloverload switch incorporating the desirable features set forth above.

Further objects and advantages of this invention will become apparent byreference to the following description and the accompanying drawing, andthe features of novelty which characterize this invention will bepointed out with particularity in the claims annexed to and forming apart of this specification.

This invention in its broadest aspects provides a thermal overloadswitch having a housing member with a cavity formed therein. A mountingmember is positioned in the cavity spaced from the bottom thereof andextending substantially across the cavity. A bimetallic element isarranged in the cavity intermediate the housing member bottom and themounting member and has one extremity secured to the mounting memberadjacent one end thereof. A movable contact is mounted adjacent theother extremity of the bimetallic element and cooperates with astationary contact. The mounting member is normally longitudinally bowedaway from the housing member bottom and means are provided forselectively deflecting the mounting member toward the housing memberbottom in order to set one characteristic of the switch, for example,the tripping temperature. The mounting member has a portion extendingtoward the bimetallic element to limit the movement thereof in order toset another characteristic or" the switch, for example, the resettingtemperature.

In the drawing, Fig. 1 is a top view of the improved thermal overloadswitch of this invention;

Fig. 2 is a bottom view of the switch of Fig. 1;

Fig. 3 is a cross sectional view taken along the line 33 of Fig. l andshowing the switch in the contacts closed position;

2,771,528 Patented Nov. 20, 1956 Fig. 4 is a view similar to Fig. 3showing the contacts in the open position; and

Fig. 5 is an exploded view in perspective, partially broken away,showing the assembly of the device of Figs. 1 to 4 inclusive.

Referring now to the figures of the drawing, the improved thermaloverload switch 1 is provided with a cup-shaped housing member 2 formedof suitable insulating material, such as a molded plastic. Housingmember 2 has a cavity 3 formed therein and an annular step 4 formed inthe inner wall 5 divides cavity 3 into upper portion 6 and lower portion7.

A mounting member 8, formed of relatively thin strip conductivematerial, such as steel, is provided, having projections 9 at one endthereof and projections 10 at the other end thereof seated on andengaging step 4, thus positioning mounting member 8 in the upper portion6 of cavity 3. Mounting member 8 has a portion 11 extending downwardlybetween extensions 9 and through an opening 12 in bottom 13 of housingmember 2. The extremity 14 of portion 11 is preferably curved, as shownin Figs. 3 and 4, to form one external terminal of the device. Theportion 11 is preferably provided with ears 15 which, after the portion11 has been inserted in opening 12, are bent inwardly engaging thebottom surface of bottom 13 thus locking mounting member 8 in place.Mounting member 8 has an indentation 16 formed therein adjacentextensions 9 for the purpose now to be described.

A bimetallic element 17 is provided, preferably having a substantiallyO-shaped configuration, as best seen in Fig. 5. A point 18 adjacent theedge of bimetallic element 17 is secured to indentation 16 in mountingmember 8 in any suitable manner, as by spot welding and an indentation19 is also formed in bimetallic element 17 opposite from point 18 andextending toward the bottom 13 of housing member 2. The indentation 19prestresses the bimetallic element 17 to provide the requisite snapaction in response to temperature changes. A movable contact 20 issecured to the underside of indentation 19 of bimetallic element 17 inany suitable manner, as by riveting or spot welding.

A terminal member 21 is provided extending through opening 22 in bottom13 of housing member 2 and having its extension 23 preferably curved asshown in Figs. 3 and 4 to provide a second external terminal. Terminalmember 21 has a portion 24 positioned in lower portion 7 of cavity 3 andgenerally disposed at right angles to the portion of member 21positioned in the opening 22. Here again, ears 25 on terminal member 21are bent inwardly after terminal member 21 is assembled in opening 22and serve to lock terminal member 21 in place. A suitable stationarycontact 26 is mounted on portion 24 of terminal member 21 and cooperateswith movable contact 20 on bimetallic element 17. It is now seen that acircuit may be provided from external terminal 14 through mountingmember 8, bimetallic element 17, movable contact 20, stationary contact26, and terminal member 21 to external terminal 23 and that bimetallicelement 17 will move in response to a predetermined ambient temperatureto separate movable contact 24) from stationary contact 26, as shown inFig. 4.

In order to render the thermal overload switch of this inventionresponsive to excessive current as well as to excessive ambienttemperature the arrangement now to be described is provided. Anotherterminal member 27 is provided positioned in opening 28 in bottom 13 ofhousing member 2. The extension 29 of terminal member 27 is alsopreferably curved to form a third external terminal. Terminal member 27has a portion 30 positioned in lower portion 7 of cavity 3 and disposedat right angles to the portion of terminal member 27. in opening 28. Asuitable heater coil 31 is provided in lower portion 7 of cavity 3 inheat transfer relationship with bimetallic element 17. Heater 31 has oneend 32 secured to the underside of portion 24 of terminal member 21 inany suitable manner, as by brazing or soldering, and has its other end33 similarly connected to portion 30 of terminal member 27. It is nowseen that a circuit may be provided from external terminal 14 throughmounting member 8, bimetallic element 17, movable contact 24),stationary contact 26, and heater 31 to external terminal N.Alternatively, one circuit may be established through external terminal14 through mounting member 8, bimetallic element 17, movable contact 29,and stationary contact 26 to external terminal 23 and another circuitestablished from external terminal. 29 through heater 31 to externalterminal 23.

It will be seen by reference to Figs. 3 and 4, that mount ing member 8is normally bowed outwardly away from bottom 13 of housing member 2, asat 34. Mounting member 8 has an opening 35 in the center thereof and athreaded opening 36 is formed in bottom 13 of housing member 2. Asuitable screw 37 seated in opening 35 in mounting member 8 with itshead engaging top surface of the mounting member and with its other endthreadingly engaging threaded opening an in bottom 13 of housing member2. it is now readily seen that mounting member 3 may be deflected towardbottom 13 by means of screw 37. A deflection of member 8 toward bottom13 increases the pressure applied by bimetallic element 17 followingengagement of movable contact 20 with stationary contact 2d and thuslowers the tripping temperature. Conversely, unscrewing screw 37 so thatmounting member 8 is deflected away from bottom 13 decreases the contactpressure and raises the tripping temperature.

In order to set the resetting temperature, mounting member 8 is providedwith a tab portion 38 between extensions 10. Tab portion 38 is bentdownwardly to limit the upward movement of bimetallic element 17 andthus to set the resetting temperature. Tab portion 38 may be bent bymeans of suitable tools in order to selectively adjust the resettingtemperature. In order to adjust the tripping temperature, the device isplaced in the ambient temperature at which the device is required totrip. The screw 37 is adjusted until bimetallic element 17 snaps fromthe position shown in Fig. 3 to the position shown in Fig. 4. in orderto adjust the resetting temperature, the device is placed in the ambienttemperature at which it is required to automatically reset and the tabportion 38 of mounting member 8 is bent downwardly until bimetallicelement 17 snaps back to the contacts closed position.

Referring specifically to Fig. 5, the improved thermal overload switchof this invention is assembled by first positioning terminal members 21and 27 with the attached heater 31 in openings 22 and 28 in bottomportion 13 of housing member 2. Portion 11 of mounting member 8 is thenpositioned in opening 12 in bottom 13 and lastly screw 37 is insertedthrough opening 35 in mounting member 8 and threaded into opening 36 inbottom 13.

it is now seen that this invention provides an extremely simpleautomatic resetting thermal overload switch incorporating only eightcomponent parts. The switch is simple to assemble, simple to adjust, andthus relatively inexpensive. While a single heater 31 is shown, it willbe readily understood that the device may be utilized without a heater31, or with more than one heater if desired.

While 1 have shown and described a particular embodiment of thisinvention, further modifications and improvements will. occur to thoseskilled in the art. I desire it to be understood therefore that thisinvention is not limited to the particular form shown and I intend inthe therein, a metallic mounting member positioned in said cavity spacedfrom the bottom thereof and extending substantially across the same,said mounting member having a portion extending through said housingmember bottom to form an external terminal, a bimetallic element in saidcavity intermediate said housing member bottom and said mounting memberand having a point thereon secured to said mounting member adjacent oneend thereof. a. movable contact mounted on said bimetallic elementopposite from said point and facing said housing member bottom, aterminal member having one end in said cavity and extending through saidhousing member bottom to form a second external terminal, a stationarycontact mounted on said one end of said terminal mem her and cooperatingwith said movable contact, another terminal member having one end insaid cavity and extending through said housing member bottom to form athird external terminal, a heater positioned in said cavity and havingits ends respectively connected to said one end of said terminalmembers, said mounting member being normally longitudinally bowed awayfrom said housing member bottom, and means for selectively deflectingsaid mounting member toward said bottom thereby to set onecharacteristic of said switch, .said mounting member having a portionextending toward said bimetallic element and adapted to limit movementof the same thereby to set another characteristic of said switch.

2. A thermal overload switch comprising a housing member of insulatingmaterial having a cavity formed therein, said housing member having astep formed in its inner wall thereby dividing said cavity into an upperlarger portion and a lower smaller portion, a metallic mounting memberpositioned in said upper cavity portion extending substantially acrossthe same and engaging said step, said mounting member having a portionextending from one end thereof and through said housing member bottom toform an external terminal, a bimetallic element in said lower cavityportion having a point thereon secured to said mounting member adjacentone end thereof, a movable contact mounted on said bimetallic elementopposite from said point and facing said housing member bottom, aterminal member having one end in said lower cavity portion andextending through said housing member bottom to form a second externalterminal, a stationary contact mounted on said one end of said terminalmember cooperating with said movable contact. said mounting member beingnormally longitudinally bowed away from said housing member bottom, saidhousing member bottom having a threaded opening formed therein, andscrew means engaging housing memher bottom opening and said mountingmember for selectively deflecting the same toward said bottom thereby toset the tripping temperature of said switch, said mounting member havinganother portion extending from the other end thereof toward saidbimetallic element, said other mounting member portion being selectivelydeflectible thereby to place a predetermined limit on the, movement ofsaid bimetallic element whereby the resetting temperature of said switchis set.

3. A thermal overload switch comprising a housing member of insulatingmaterial having a cavity formed therein, a metallic mounting memberpositioned in said cavity spaced from the bottom thereof and extendingsubstantially across the same, said mounting member having a portionextending from one end thereof and through said housing member bottom toform an external terminal, a substantially O-shaped bimetallic elementin said. cavity intermediate said housing member bottom and saidmounting member and having a point thereon secured to said mountingmember adjacent one end thereof, a movable contact mounted on saidbimetallic element opposite from said point and facing said housingmember bottom, a terminal member having one end in said cavity extendingthrough said housing member bottom to form a second external terminal, astationary contact mounted on said one end of said terminal member andcooperating with said movable contact, said mounting member beingnormally longitudinally bowed away from said housing member bottom, saidhousing member bottom having a threaded opening formed therein, andscrew means engaging said housing member bottom opening and saidmounting member for selectively deflecting the same toward said bottomthereby to set the tripping temperature of said switch, said mountingmember having another portion extending from the other end thereoftoward said bimetallic element, said other mounting member portion beingselectively deflectible thereby to place a predetermined limit on themovement of said bimetallic element whereby the resetting temperature ofsaid switch is set.

4. A thermal overload switch comprising a housing member of insulatingmaterial having a cavity formed therein, a metallic mounting memberpositioned in said cavity spaced from the bottom thereof and extendingsubstantially across the same, said mounting member having a portionextending from one end thereof and through said housing member bottom toform an external terminal, a substantially O-shaped bimetallic elementin said cavity intermediate said housing member bottom in said mountingmember and having a point thereon secured to said mounting memberadjacent one end thereof, a movable contact mounted on said bimetallicelement opposite from said point and facing said housing member bottom,a terminal member having one end in said cavity extending through saidhousing member bottom to form a second external terminal, a stationarycontact mounted on said one end of said terminal member and cooperatingwith said movable contact, another terminal member having one end insaid cavity and extending through sail housing member bottom to form athird external ter minal, a heater positioned in said cavityintermediate said bimetallic element and said housing member bottom andhaving its ends respectively connected to said one end of said terminalmembers, said mounting member being normally longitudinally bowed awayfrom said housing member bottom, said housing member bottom having athreaded opening formed therein, and screw means engaging said housingmember bottom opening and said mounting member for selectivelydeflecting the same toward said bottom thereby to present the trippingtem perature of said switch, said mounting member having another portionextending from the other end thereof toward said bimetallic element,said other mounting member portion being selectively deflectible therebyto place a predetermined limit on the movement of said bimetallicelement whereby the resetting temperature of said switch is set.

5. A thermal switch comprising a housing member of insulating materialhaving a cavity formed therein, said housing member having a step formedin its inner wall thereby dividing said cavity into an upper largerportion and a lower smaller portion, a metallic mounting memberpositioned in said upper cavity portion extending substantially acrossthe same and engaging said step, said mounting member having a portionextending from one end thereof and through said housing member bottom toform an external terminal, a substantially O-shaped bimetallic elementin said lower cavity portion and having a point thereon secured to saidmounting member adjacent one end thereof, said bimetallic element havingan indentation formed therein opposite said point and extending towardsaid housing member bottom, a movable contact mounted on saidindentation and facing toward said housing member bottom, a terminalmember having one end in said lower cavity portion extending throughsaid housing member bottom to form a second external terminal, astationary contact mounted on said one end of said terminal member andcooperating with said movable contact, another terminal member havingone end in said lower cavity portion and extending through said housingmember bottom to form a third external terminal, a heater positioned insaid lower cavity portion intermediate said bimetallic element and saidhousing member bottom and having its ends respectively connected to saidone end of said terminal members, said mounting member being normallylongitudinally bowed away from said housing member bottom, said housingmember bottom having a threaded opening formed therein, and screw meansengaging said housing member bottom opening and said mounting member forselectively deflecting the same toward said bottom thereby to reset thetripping temperature of said switch, said mounting member having anotherportion extending from the other end thereof toward said bimetallicelement, said other mounting member portion being selectivelydeflectible thereby to place a predetermined limit on the movement ofsaid bimetallic element whereby the resetting temperature of said switchis set.

References Cited in the file of this patent UNITED STATES PATENTS1,511,352 Miller Oct. 14, 1924 1,621,056 Bradshaw Mar. 15, 19272,044,147 Bletz June 16, 1936 2,587,789 Talmadge et al Mar. 4, 19522,611,855 Turner Sept. 23, 1952 2,647,189 De Puy July 28, 1953 2,651,696Seely Sept. 8, 1953

